This invention relates generally to wear resistant decorative laminates having excellent scratch and abrasion resistance. More particularly, this invention relates to wear resistant, decorative laminates including a protective coating thereon which comprises a mixture of different sized mineral particles.
Decorative laminates are known in the art for use as surfaces for counter tops, table tops, furniture, and the like. Such decorative laminates are typically comprised of a core formed from a plurality of sheets of Kraft paper which are impregnated with a resin. Positioned above the core is a decorative sheet which is typically a cellulose pigmented paper containing a print, pattern, or solid color which may also be impregnated with a resin. The decorative sheet is generally covered with a transparent or semi-transparent protective overlay sheet comprising a cellulose paper impregnated with a phenolic resin such as melamine-formaldehyde. The overlay sheet protects the decorative sheet from abrasion, scratches, chemicals, burns, and the like.
The decorative laminates are typically made by stacking the core, decorative sheet, and overlay sheet, and then inserting the stack between pressing plates at a temperature and pressure sufficient to cause the laminating resins to flow and cure between the respective layers. When making the decorative laminates, it is often desirable to coat the back (under) side and/or the top side of the overlay sheet with a resin containing small particles of abrasive materials such as silica or alumina in order to improve the abrasion resistance of the laminate.
However, it has been found that the incorporation of such abrasive minerals into the overlay sheet can cause severe damage to the delicate, highly polished or intricately etched surfaces of the press plates. Many attempts have been made to overcome this problem. See, for example, U.S. Pat. No. 5,558,906, which teaches the use of an abrasion resistant coating comprising a thermoset resin, a mixture of alumina particles, a silane coupling agent, and a thickening agent which functions to suspend the alumina particles and protect the press plates. Others have addressed the problem by treating the surfaces of the press plates to make them more resistant to scratching. See U.S. Pat. No. 6,656,329. Still others have attempted to use smaller sized mineral particles in an effort to protect the plates. See U.S. Pat. No. 5,141,799, which teaches the use of amorphous silica powder having a particle size range from about 0.01 to 0.05 microns. However, the particles must be applied as an agglomerate having a composite size between 12 to 30 microns in order to provide sufficient abrasion resistance.
Accordingly, there is still a need in the art for a coating for use on decorative laminates which imparts scratch and abrasion resistance to the laminate but does not damage press plates during manufacture of the laminate.